Studies of the tryptophan synthase alpha-2 beta-2 complex serve as a model for studies of more complicated multienzyme complexes. Several active site residues previously identified in this laboratory have now been located in a large cyanogen bromide fragment of the beta-2 subunit. The primary sequence of the first 104 residues of the beta chain which contain this fragment has been determined. Two fragments of the alpha subunit which result from limited tryptic proteolysis of the alpha-2 beta-2 complex have been separated, characterized, and shown to recombine. The amino terminal fragment, alpha-1, contains residues 1-188 and has a molecular weight of 20,500; the carboxy terminal fragment, alpha-2, contains residues 189-268 and has a molecular weight of 8,300. The fragments are demonstrated to be independent folding domains which have no enzymatic or binding properties until recombined.